Over 160,000 active dental practitioners provide care to more than 83 million patients each year in the US, yet there is currently little to no understanding about type, frequency, or severity of adverse events in that context. Medical adverse events (AEs) are one of the leading causes of death in the US, and those that originate in the hospital setting have gained prominent attention from academic, healthcare, and government institutions and organizations. Much less is known about the safety of ambulatory care settings in general, and this is especially true in dentistry. This gap is troubling because a large proportion (65.5%) of the U.S. population goes to the dentist at least once a year and because case reports in the literature indicate that serious adverse events do happen in the dental office. The inherent risk of dental care is not surprising, given that dentists, like physicians, routinely perform highly technical procedures in complex environments, work in teams, and use a multitude of devices and tools. To minimize these threats to patient safety, we must first understand their basic epidemiology, both in terms of their incidence and the extent to which they affect different populations. In Aim 1, we will conduct large- scale dental health record audits in order to identify the incidence of adverse events and with which procedures and devices these events were associated. Aim 2 will reveal the extent to which the incidence of these events varies by race, ethnicity, and age. In Aim 3, we will address a further challenge in ambulatory care settings that results from the fragmentation of care. In particular, we will determine how many additional adverse events originating in the dental office can be identified if both the dental and medical health records of patients are reviewed. The research that we will conduct will leverage our extensive preliminary work in the dental setting, which has led to tested dental record safety audit tools and procedures, as well as classification schemes to describe both the type and severity of adverse events in the dental office. We expect that in addition to the specific deliverables and products of this research, this developmental project wil greatly raise awareness of the importance of patient safety in dentistry and will catalyze a novel line of dental clinical, quality improvement, and health economics research. Relevance: Adverse events in medicine are a major source of preventable death and injury. As a profession, dentistry is essentially flying blind with to respect to the hazards of care. Identifying and characterizing adverse events in the dental clinic is the first step toward addressing these events, which will advance our collective public health.